Language disorders in Parkinson's disease (PD) are a) more frequent than previously suspected, b) under- diagnosed and under-treated and c) increase disability and caregiver burden when present - yet no properly controlled, prospective studies of language problems in PD have yet been conducted. We propose to conduct just such a longitudinal study of language changes in PD and to assess the impact of these changes on daily functioning in affected patients. We will focus on "pragmatic" language processes as these concern the use of language in social context and recent reports (McNamara &Durso, 2003) document significant deficits in selected aspects of pragmatic language processing in mid-stage PD patients. We will test the hypothesis that pragmatic language/communication skills are impaired even in early PD and are significantly related to cognitive, affective (e.g., depression) and social dysfunction associated with PD. We propose a longitudinal research design assessing language functions as well as cognitive, affective and social functions in a group of 54 newly diagnosed PD patients. Patients will be assessed three times over the course of the 5-year study (approximately every 1.5 years). Mixed effects regression modeling will be applied to the data to derive quantitative estimates of key indicators of language trajectories of PD patients and the relations of these trajectories to changes in disease severity, medication dosing regimes, cognitive, affective and social functions. Data from this project will 1) give us a clear picture of the nature of the pragmatic deficit in PD as well as its cognitive and neuropsychological correlates;2) clarify the role neo-striatal/prefrontal neural systems in mediation of pragmatic functions;3) clarify the extent to which pragmatic social communication deficits are related to the cognitive and social deficits of PD;and 4) establish benchmark data on neural, cognitive and affective correlates of fundamental pragmatic functions which could potentially be used to develop more effective clinical treatments for disorders of social communication.